Electrical current transducers for current sensing applications typically comprise a magnetic core made of a high permeability magnetic material, surrounding a central cavity through which passes a primary conductor carrying the current to be measured. The magnetic core may typically have a generally rectangular or circular shape and be provided with an air-gap in which a magnetic field sensor, such as a Hall effect sensor, is positioned. The magnetic flux generated by the electrical current flowing in the primary conductor is concentrated by the magnetic core and passes through the air-gap. The magnetic field in the air-gap is representative of the primary current. In current transducers of the open-loop type, the magnetic field sensor in the air-gap generates an image of the current to be measured that represents the measurement signal. In current sensors of the closed-loop type the magnetic field sensor is connected in a feed-back loop to a coil that is typically wound around a portion of the magnetic core in order to generate a compensation current that tends to cancel the magnetic field generated by the primary conductor. The compensation current thus represents an image of the current to be measured. A fluctuating voltage or current in the primary conductor may adversely influence the measurement signal because of the capacitive coupling between the primary conductor and the magnetic core. A difference in potential between the magnetic core and the measurement signal processing circuit may also adversely influence the measurement signal and it is therefore common to connect the magnetic circuit electrically to a reference voltage, namely ground, of the signal processing circuit.
In certain conventional current transducers, a ground terminal is crimped to the magnetic core for establishing the ground connection. It may also be known to solder a ground connection to the magnetic core, or employ other direct electrical connections.
The electrical connection to the magnetic core increases the cost of manufacturing and assembling the magnetic core, and may also affect the magnetic properties (magnetic permeability) of the material of the core. Also, the electrical connection to the magnetic core, depending on the type of core and application, may be susceptible to rupture, for example through wear and vibrations, leading to a faulty electric current measurement signal that goes unnoticed, or requires replacement of the sensor.
It is known to provide a ground plane on a circuit board on which the magnetic core is mounted, as described in JP0462482. In view of the large surface area of the circuit board and the relatively high mass of the magnetic core, this configuration is however costly and not sufficiently robust for certain applications, in particular when subjected to vibration, mechanical shocks and large thermal operating ranges